The underlying hypothesis in this work is that cross-sectional images (elastograms) which are related to the local bulk Young's moduli of soft tissue [Ophir et al, 1991] convey new information which could substantially increase the capability to display and interpret tissue structure in corresponding conventional sonograms. In order to test this hypothesis, we propose the following specific aims: (1) Investigate the factors and tradeoffs which influence the sensitivity, dynamic range, resolution and signal-to-noise ratio performance of elastograms. (2) Identify and investigate the origin of artifacts which may be present in elastograms. (3) Generate elastograms of tissue mimicking phantoms and of normal bovine muscle in vitro. Compare the elastographically derived elasticity values to elasticity values obtained independently. (4) Compare the sonographic and elastographic visualization of tissue structures in human prostates in vitro. (5) Measure and catalog the elastic properties of breast and prostate tissues in vitro. Preliminary work has shown that (1) there is a measurable range of elasticities associated with normal tissues (and presumably also with pathological tissues); (2) elastography is capable of producing elasticity based images (elastograms), which are of sufficient resolution and sensitivity to visualize the complex elastic structure of heterogeneous soft tissues in vivo; and (3) the structural information of tissue displayed by elastography may not be otherwise obtainable. The work proposed here is intended to provide answers to some fundamental questions; these questions pertain to all aspects of elastography, starting from the basic physics, through signal processing and optimization, and ending in image formation and interpretation. The answers are expected to put elastography on a firm theoretical and experimental foundation, thereby allowing expansion of capabilities of diagnostic ultrasound imaging.